The present invention relates generally to gas turbine engines, and, more specifically, to sealed turbine frames therein.
In a typical gas turbine engine, air is compressed in a compressor, mixed with fuel and ignited to produce combustion gases in a combustor, and channeled downstream through one or more stages of turbine nozzles and rotor blades. The rotor blades extend radially outwardly from a disk which is joined to a shaft for powering the compressor or fan. The shaft is supported by bearings from a bearing support which forms part of a turbine frame.
An exemplary turbine frame disposed downstream of a last rotor stage for example, includes a plurality of circumferentially spaced apart supporting struts which extend radially between inner and outer annular bands. The bearing support is fixedly joined to the inner band, and the outer band is fixedly joined to an outer casing of the engine.
Surrounding each of the struts is a hollow fairing which is suitably provided with pressurized cooling air bled from the compressor for cooling the turbine frame from the heating effects of the hot combustion gases which flow axially therethrough. The fairings are joined at their inner and outer ends to annular members defining corresponding inner and outer flowpaths between which the combustion gases flow. With each of the fairings suitably surrounding respective ones of the struts, the fairing assembly is allowed to float relative thereto with unrestrained differential thermal expansion and contraction movement. During operation, the fairings are directly bathed in the combustion gases and therefore expand radially outwardly at a greater rate than the struts protected therein. The cooling air channeled through the fairings cools the fairings as well as the struts and further affects the differential thermal movement between the fairings and the struts.
Since the inner flowpath is joined to the fairings and is itself subject to heating by the combustion gases, it also expands and contracts at a different rate than that of the struts. Since the cooling air is channeled radially inwardly through the fairings and the inner flowpath, suitable seals are required to prevent or control leakage from the cooling circuit of the turbine frame while permitting or accommodating differential thermal movement between the components.
In one conventional design, an inner cylindrical ring forms an extension of the bearing support and extends axially forwardly from the inner band of the struts. A generally T-section annular sliding axial seal surrounds the inner ring, with the head of the T forming a seal therewith. The base of the T extends radially outwardly and defines a tongue which is radially received in an annular groove of a radial seal which is fixedly joined to the fairing inner flowpath. In this arrangement, the radial seal accommodates differential radial expansion and contraction between the inner flowpath and the bearing support, and the axial seal accommodates axial differential movement therebetween.
Both these radial and axial seals are subject to frictional wear during operation as the components thereof slide during differential movement, which results in increased leakage through the seals over time. Accordingly, additional cooling air must be provided, which correspondingly decreases the overall engine efficiency. And, the double seal assembly is relatively complex and includes several components which require separate manufacturing processes, with attendant cost thereof.